1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier or printer. More specifically, the present invention relates to an image forming apparatus provided with a member for cleaning toner remaining on an image bearing member after transferring a toner image to a transfer incurring material.
2. Related Background Art
Heretofore, for example, in an image forming apparatus of an electrophotographic process, an electrostatic latent image in accordance with image information is formed on an electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive member”) as an image bearing member, developing means supplies toner (a developer) to the photosensitive member in accordance with this electrostatic latent image, and thus a toner image (a developer image) is formed. Then, this toner image is finally transferred to a transferring material, for example, to a recording sheet, an OHP sheet, or the like, followed by fixing, and thus a permanent image is obtained.
Among color image forming apparatuses using the electrophotographic process, there is one in which toner images of different colors are sequentially formed on a single photosensitive member and these toner images are transferred to a transferring material, or the toner images are transferred to an intermediate transfer member sequentially in an overlapping manner and then collectively transferred to the transferring material, followed by fixing, thus obtaining a color image. Moreover, there is one, in which toner images of colors different from one another are formed on a plurality of photosensitive members and these toner images are transferred to the transferring material, or the toner images are transferred to the intermediate transfer member sequentially in an overlapping manner and collectively transferred to the transferring material, followed by fixing, thus obtaining a color image.
In these days, as such an image forming apparatus of the electrophotographic process, a multiple function machine combining all output terminals such as a copier, a printer, and a fax machine have come to be widely accepted in the market. As such a network-capable output terminal, the electrophotographic process has been widely accepted; however, a duty cycle of a main body of the apparatus has come to be cited as one problem. The duty cycle means the limit number of image recording sheets up to which the main body of the apparatus continues to operate normally without any maintenance by a service person. The life of the photosensitive member is cited as the greatest rate-determining factor of the duty cycle.
Moreover, from the viewpoint of ecology, it is required that waste be eliminated, that is, it is required that consumables be reduced, that the life of the consumables be extended, and that the reliability be enhanced.
Furthermore, digitization of the image forming apparatus has progressed from a conventional analog apparatus, and it is required that the main body of the apparatus be equivalent or less in cost to the analog apparatus. Heretofore, in the copier and the printer, monochrome machines have been the mainstream; however, in recent years, the demand for full color image formation of originals or output files has increased dramatically even in offices. Accordingly, there is a demand for a full-color image forming apparatus which, in addition to being a digital apparatus equivalent to the analog machine in cost, is equivalent to monochrome machines in terms of the cost of the main body thereof and running cost. For this purpose, a technology capable of remarkably lowering TCO (Total Cost of Ownership) is desired.
Under such circumstances, an amorphous silicon photosensitive member as the image bearing member has come to be used often because hardness thereof is high (1000 Kg/m2 or more in Vickers hardness according to a JIS standard), and because this amorphous silicon photosensitive member is excellent also in durability, heat resistance, and environmental stability. Particularly, in a monochrome high-speed machine for which high reliability is required, the amorphous silicon photosensitive member has come to be essential. Usually, the life of the amorphous silicon photosensitive member as represented by the number of prints necessitating replacement of the photosensitive member is more than one digit higher than that of an OPC photosensitive member. Specifically, the life of the amorphous silicon photosensitive member is equivalent to that of the main body of the apparatus, which also brings an effect of waste reduction. Furthermore, unlike a process cartridge using the OPC photosensitive member, manpower for collection and recovery thereof is not required.
If such a technology using the amorphous silicon photosensitive member mounted on the high-speed machine can be implemented on the full-color image forming apparatus, preferably, it is possible to realize an image forming apparatus which cannot only achieve the duty cycle and low running cost of the high-speed machine for a monochrome print but also carry out a color print. Particularly, for a user frequently making the monochrome print, in order to achieve the duty cycle and the low running cost which are equivalent to those of the monochrome high-speed machine, it is considered to be the most preferable to mount the amorphous silicon photosensitive member on a so-called full-color image forming apparatus of a one-drum system, which uses a rotary developing device having a plurality of developing means mounted on a rotator, and performs development on a single photosensitive member while sequentially switching among the developing means (for example, a drum-type photosensitive member).
In the image forming apparatus repeating the step of transferring a transferable toner image formed on a surface of the photosensitive member to the transferring material mainly made of paper or the intermediate transfer member, it is essential to sufficiently remove adhesion matter such as toner remaining on the photosensitive member without being transferred to a transfer incurring member during the transfer (transfer residual toner) whenever such adhesion matter is generated.
For this reason, many proposals have been made concerning cleaning means for the photosensitive member (for example, in Japanese Patent Application laid-Open Nos. S56-55979 and H9-2 18625). Among them, one which scrapes off the adhesion matter by a blade-shaped cleaning member made of an elastic material such as urethane rubber, that is, a cleaning blade, has been widely put into practical use for its simple configuration, compactness, and low cost and also for its excellent adhesion matter removing function. As a rubber material of the cleaning blade, the urethane rubber is generally used, which is high in hardness, rich in elasticity, and excellent in abrasion resistance, mechanical strength, oil resistance, and ozone resistance.
In order to extend the life of the photosensitive member and to enhance the reliability thereof from the viewpoint of achieving the duty cycle, the low running cost, and the reduction of the waste which are equivalent to those of the monochrome high-speed machine, the removal of the adhesion matters from the surface of the photosensitive member becomes a problem. It is not oniy the toner that adheres onto the surface of the photosensitive member and affects image quality. Adhesion matter (foreign matter) adhered onto the surface of the photosensitive member because of fine paper powder generated from paper used as the transferring material in almost all cases, an organic component precipitated therefrom, generation of corona occurring due to the presence of a high-pressure member in the apparatus, and the like, may cause a reduction in resistance particularly under a high-humidity environment to prevent a clear electrostatic latent image from being formed. This is considered to be the factor causing a deterioration of the image quality.
It is known that such an image deterioration phenomenon as described above is prone to occur in the case of an amorphous silicon photosensitive member which is configured to form a film by glow discharge decomposition of silanes.
In order to avoid such a defect, particularly in the case of using a one-component magnetic developer as the toner, there has been proposed one in which a magnet roller is disposed, in the cleaning device, on an upstream side of the cleaning blade as viewed in a running direction of the photosensitive member, a magnetic brush is formed by a part of toner collected by the cleaning device, the magnetic brush is brought into contact with the surface of the photosensitive member to resupply the magnetic toner thereto, and the above-mentioned variety of adhesion matter (foreign matter) are removed in a rubbing manner by means of a polishing action of toner particles in an abutting region of the cleaning blade.
As compared with a method of rubbing the surface of the image bearing member by a separately prepared polishing member such as a web and a rubber roller, the cleaning means using such a magnetic brush as described above involves less localization of the polishing action on the surface of the photosensitive member, and therefore less deformation of the surface of the photosensitive member.
Together with the polishing method using the above-described magnetic brush, there may be used auxiliary means of, for example, disposing a heater for the photosensitive member to lower humidity in a periphery thereof also at night and during standby, thereby preventing the resistance of the surface of the photosensitive member from being lowered. In such a way, a certain effect is obtained for hindering the image deterioration caused by the variety of adhesion matter as described above.
Moreover, for example, in the case of employing an intermediate transfer member in a color image forming apparatus such as a full-color image forming apparatus of the one-drum system, in order to realize the above-described duty cycle and low running cost which are equivalent to those of the monochrome high-speed machine, it is necessary to enhance the reliability of the intermediate transfer member. Here, as in the case of the above-described photosensitive member, removal of adhesion matter from a surface of the intermediate transfer member becomes a problem.
For cleaning means for removing the adhesion matter, such as the toner, which remain on the intermediate transfer member after transferring the toner image to the transferring material, many proposals have been made heretofore. Among them, as in the case of the above-described photosensitive member, one which scrapes off the adhesion matter by a blade-shaped cleaning member made of an elastic material such as the urethane rubber, that is, a cleaning blade, has been widely put into practical use for its simple configuration, compactness, and low cost and also for its excellent adhesion matter removing function. As a rubber material of the cleaning blade, the urethane rubber is generally used, which is high in hardness, rich in elasticity, and excellent in abrasion resistance, mechanical strength, oil resistance, and ozone resistance.
However, some problems are pointed out in the conventional method for cleaning the members to be cleaned in the image forming apparatus, such as the photosensitive member and the intermediate transfer member.
A problem caused by separating/abutting of the cleaning blade is posed. In the case where the degrees of adhesion and affinities between the cleaning blade and the surface of the image bearing member and between the adhesion matter on the image bearing member and the surface of the image bearing member are increased, when the cleaning blade is attached and/or detached, that is, when the cleaning blade is made to abut on the image bearing member or is separated therefrom, the speed of the intermediate transfer member becomes uneven, causing misregister of colors. Furthermore, vibrations may be applied to the image bearing member due to the wear of the blade caused by an impact given thereto when the blade is made to abut on the image bearing member or by the frictional force with the image bearing member, and the like, or due to the impact applied when the blade is made to abut thereon, causing an image failure.